IBM System/370

IBM System/370
Company type	Product line
Industry	Computer hardware
Predecessor	IBM System/360
Founded	June 30, 1970; 56 years ago
Headquarters	Armonk, New York, United States
Products	Mainframe computers
Owner	IBM

The IBM System/370 (S/370) series, launched on June 30, 1970, encompasses a spectrum of computing systems ranging from entry-level units to full-scale mainframes. It was developed as the successor to the System/360 family. Maintaining substantial backward compatibility with the S/360, the S/370 facilitated straightforward transitions for existing users while offering enhanced performance as a principal advantage.

Initial System/370 models replaced the System/360’s Solid Logic Technology hybrid integrated circuits with more sophisticated monolithic integrated circuits, known as Monolithic System Technology (MST). This advancement in packaging density allowed features that were previously optional—such as floating-point capabilities—to become standard components. Additionally, the S/370 introduced several new machine instructions.

At the time of introduction, the absence of virtual memory functionality sparked debate; IBM responded in 1972 by releasing the System/370 Advanced Function along with dynamic address translation (DAT) hardware. Following this development, later models incorporated this capability and were accompanied by new operating systems designed to utilize virtual memory. The product line expanded incrementally over time, often distinguished by processor model numbers. A significant upgrade arrived in 1988 with the ESA/370 extensions, which allowed multiple virtual address spaces and fast switching between them.

Throughout the 1970s and 1980s, the System/370 served as IBM’s premier mainframe platform. In September 1990, it was replaced by the System/390, built upon the ESA/390 architecture. The System/390 introduced enhanced hardware virtualization features that enabled concurrent execution of multiple operating systems.

Evolution

The debut of the original System/370 lineup occurred on June 30, 1970, featuring Models 155 and 165 slated for delivery to customers in early 1971. The Model 155 was first shipped in January 1971. Over its approximate two-decade production run, the System/370 experienced numerous architectural enhancements.

Among the notable features newly introduced or standardized on the System/370 were:

Branch and Save
Channel Indirect Data Addressing
Channel-Set Switching
Clear I/O
Command Retry
Commercial Instruction Set (previously optional on S/360)
Conditional Swapping
CPU Timer and Clock Comparator
Dual-Address Space (DAS)
Extended-Precision Floating Point (formerly available on select S/360 models)
Extended Real Addressing
External Signals
Fast Release
Floating Point (previously optional)
Halt Device
I/O Extended Logout
Limited Channel Logout
Move Inverse (offered as RPQ on S/360)
Multiprocessing (present on some S/360 models and IBM 9020)
PSW-Key Handling
Recovery Extensions
Segment Protection
Service Signal
Start-I/O-Fast Queuing (SIOF)
Storage-Key-Instruction Extensions
Storage-Key 4K-Byte Block
Suspend and Resume
Test Block
Translation (Dynamic Address Translation distinct from S/360 Model 67)
Vector (exclusive to IBM 3090)
31-Bit IDAWs

Initial models

The earliest System/370 computers—the Model 155 and Model 165—built upon but did not overhaul the architecture established by the System/360 in 1964. Key modifications included:

Introduction of thirteen new instructions, most notably:
- MOVE LONG (MVCL) and COMPARE LOGICAL LONG (CLCL), which extended data operation limits from 256 bytes to as much as 16 MB;
- SHIFT AND ROUND DECIMAL (SRP), designed for multiplying or dividing packed decimal quantities by powers of ten with rounding capabilities;

Optional support for 128-bit hexadecimal floating-point arithmetic, a feature first seen in the System/360 Model 85;
Implementation of a higher precision time-of-day clock;
Compatibility with block multiplexer channels introduced alongside the System/360 Model 85.

All emulator functionalities were intended to function under standard operating systems, with IBM providing documentation for integrated emulator software.

These first-generation machines utilized core memory technology and did not incorporate virtual storage support due to their lack of Dynamic Address Translation (DAT) hardware.

Logic technology

Every System/370 variant utilized IBM's Monolithic System Technology (MST), a type of monolithic integrated circuit, categorizing these machines as third-generation computers. MST provided a circuit density that was four to eight times greater and reliability exceeding tenfold compared to the earlier Solid Logic Technology (SLT) used in the System/360.

Monolithic memory

IBM unveiled the System/370 Model 145 on September 23, 1970, marking the first model to incorporate semiconductor main memory built from monolithic integrated circuits, with shipments planned for late summer 1971. This memory innovation was subsequently adopted across all following S/370 models.

Virtual storage

In 1972, IBM reversed its initial stance by introducing virtual storage support through the "System/370 Advanced Function" announcement. This update, made on August 2, 1972, included several key elements:

Address relocation hardware implemented on all S/370 machines except the original 155 and 165 models
The launch of new S/370 models 158 and 168 equipped with address relocation capabilities
Introduction of four operating systems: DOS/VS (DOS with virtual storage), OS/VS1 (OS/360 MFT with virtual storage), OS/VS2 Release 1 (SVS - Single Virtual Storage), OS/VS2 Release 2 (MVS - Multiple Virtual Storage) scheduled for March 1974, and VM/370 (a reimplementation of CP/CMS)

Virtual storage functionality had been present on the S/370-145 since June 1971 by utilizing associative memory in microcode for DOS compatibility and dynamic address translation. Although virtual storage was initially excluded from the S/370 introduction, practical experience at Cambridge Scientific Center prompted IBM to reconsider. The microcode design of the Model 145 allowed virtual storage implementation without significant hardware modifications, yet IBM did not officially disclose this feature. Existing S/370-145 owners could operate DOS/VS or OS/VS1 without requiring hardware enhancements.

After the August 1972 announcement, upgrades adding address relocation hardware (DAT units) were discreetly made available for the S/370-155 and -165 models—rebranded as S/370-155-II and -165-II—but only to current customers. IBM preferred that users transition to the newer S/370-158 and -168 models instead. These upgrades were expensive, ranging from $200,000 to $400,000, involved lengthy lead times, and saw limited acceptance since many clients leased their systems through third parties. As a result, numerous users continued operating original 155 and 165 machines running MVT until lease expiration, sometimes extending over several years. This scenario considerably delayed widespread adoption of OS/VS2 MVS both externally among users and internally within IBM.

Subsequent enhancements

Subsequent architectural improvements concentrated on enlarging both physical and virtual memory capacities to accommodate heavier workloads and evolving customer requirements amid declining memory costs consistent with Moore's Law. Preserving backward compatibility remained a central focus throughout IBM mainframe evolution.

Operating system-specific enhancements such as Extended Control Program Support (ECPS) improved performance in OS/VS1, MVS, and VM by shortening execution paths for frequently used operations.
Introduced in 1981 with the IBM 3033, the Dual Address Space (DAS) capability allowed privileged software to transfer data directly between address spaces more efficiently by removing buffer allocation overhead. DAS was later extended to processors including the 43xx series, 3031, and 3032 models, with MVS/System Product (MVS/SP) Version 1 leveraging this functionality.
In October 1981, processors like the 3033 and 3081 incorporated "extended real addressing," enabling physical addressing up to 26 bits while individual address spaces remained capped at 24 bits. This feature was subsequently adopted by systems such as the 4381 and 3090.
Early in 1983, the System/370 Extended Architecture (S/370-XA) debuted on the 3081 and 3083 processors, dramatically expanding virtual address spaces from 24-bit to 31-bit and real addresses up to 31 bits alongside a comprehensive redesign of the I/O architecture.
February 1988 brought Enterprise Systems Architecture/370 (ESA/370) for enhanced versions of the 3090 and 4381 models, introducing sixteen new 32-bit access registers, broader addressing modes, and improved handling of concurrent multiple address spaces.
On September 5, 1990, IBM launched Enterprise Systems Architecture/390 (ESA/390), which maintained full upward compatibility with ESA/370 while further advancing mainframe architectural capabilities.

Dual address space

In 1981, IBM enhanced the System/370 by adding a dual-address-space capability, allowing programs to simultaneously access two distinct address spaces. Control Register 1 contains the segment table origin (STO) for the primary address space, while Control Register 7 holds the STO for the secondary address space. The processor can function in either primary-space or secondary-space mode: in primary mode, instructions and data are fetched from the primary space; in secondary mode, operands are retrieved from the secondary space. However, instruction fetches in secondary mode are unpredictable and must be identically mapped in both address spaces. Mode transitions occur through the SET ADDRESS SPACE CONTROL instruction, and data transfers between spaces are performed using MOVE TO PRIMARY and MOVE TO SECONDARY instructions.

Each address space is identified by an address-space number (ASN), which serves as an index into a two-level table structure similar to that of a page table. Table entries include presence indicators, access rights, segment table start addresses, segment lengths, and additional metadata. The current secondary address space is selected via the SET SECONDARY ASN instruction by specifying its ASN.

Extended real addressing

Initially, System/370 supported physical addresses limited to 24 bits, restricting memory to a maximum of 16 MB. Page table entries combined a 12-bit or 13-bit page frame number with an offset to form these addresses. The introduction of extended real addressing expanded this limit to 26 bits, thereby increasing physical memory capacity to 64 MB by repurposing two reserved bits within page table entries for 4 KB pages. This enhancement requires that address translation be enabled and applies exclusively when using 4 KB page sizes.

Chronological listing of models (table)

The following table provides an overview of key S/370 series and models, highlighting the principal architecture associated with each. Many models supported multiple architectures; for instance, the 308x processors were initially released with System/370 architecture but later offered XA support. Similarly, some models such as the 4381 gave customers the option to choose between System/370 or XA (and later ESA) through microcode configuration.

IBM documents used the designation "System/370-compatible" to describe certain products. Outside IBM, this term was more frequently applied to systems produced by Amdahl Corporation, Hitachi, and others that could run S/370 software. IBM’s use of this label may have been intended to minimize the perceived competition from these plug compatible manufacturers (PCMs), who posed a challenge to IBM’s hardware market dominance.

Initial year of series	Architecture	Market segment	Series	Models
1970	System/370 (without DAT)	high-end	System/370-xxx	-155, -165, -195
1970	System/370 (with DAT)	mid-range		-145 and -135
1972	System/370	high-end		-158 and -168
		entry-level		-115 and -125
		mid-range		-138 and -148
1977	System/370-compatible	high-end	303x	3031, 3032, 3033
1979		entry/mid-range	43xx	4331, 4341, 4361
1980		high-end	308x	3081, 3083, 3084
1981	System/370-XA	high-end	308x	3081, 3083, 3084
1983		mid-range	4381	4381
1986		high-end	3090	-120 through -600
1986	System/370-compatible	entry-level	937x	9370, ...
1988	ESA/370	high-end	ES/3090	ES/3090
1988	ESA/370	mid-range	ES/4381	-90, -91, -92

Models categorized by Model number (comprehensive)

IBM identified the following eleven System/370 models, each with a three-digit designation:

System/370 Model 115

Introduced on March 13, 1973, the IBM System/370 Model 115 was aimed at users familiar with IBM's System/3, the 1130 system, and System/360 Models 20, 22, and 25. It came standard with at least two directly connected IBM 3340 disk drives, with expansion capacity up to four drives. The central processor supported either 64K or 96K bytes of main memory and optionally included a 360/20 emulator. This model was retired from the market on March 9, 1981.

System/370 Model 125

The IBM System/370 Model 125, announced on October 4, 1972, was equipped with two to four directly attached IBM 3333 disk storage units, offering up to 400 million bytes of online storage. Memory configurations were available in either 96K or 128K bytes. The Model 125 was discontinued on March 9, 1981.

System/370 Model 135

Announced on March 8, 1971, the IBM System/370 Model 135 provided four options for main memory capacity and incorporated emulation capabilities for the IBM 1400 series (including models 1401, 1440, and 1460). Its console featured a reading mechanism that allowed microcode updates and the addition of new functionalities. The Model 135 was phased out on October 16, 1979.

System/370 Model 138

Revealed on June 30, 1976, the IBM System/370 Model 138 offered memory sizes of either 512K or one megabyte—twice the maximum memory available in the Model 135. Customers could upgrade their existing Model 135 units onsite to match the performance level of the Model 138. This model was withdrawn from service on November 1, 1983.

System/370 Model 145

The IBM System/370 Model 145, announced September 23, 1970—shortly after the Models 155 and 165—and first delivered in June of the following year, was notable for being the first System/370 to utilize monolithic main memory available in six different capacities. A portion of this memory, termed "Reloadable Control Storage" (RCS), was loaded from a disk cartridge containing microcode that implemented instructions, I/O channels, and optional features such as emulation of earlier IBM systems.

The Model 145 ceased production on October 16, 1979.

System/370 Model 148

The IBM System/370 Model 148 shared its announcement and withdrawal dates with the Model 138. Similar to how a Model 135 could be upgraded in the field, a System/370 Model 145 could also be enhanced onsite to achieve performance comparable to the Model 148. These upgraded systems were designated as Models 135-3 and 145-3.

System/370 Model 155

The IBM System/370 Models 155 and 165 were jointly announced on June 30, 1970, marking the initial entries in the System/370 line. Both lacked a DAT box and were limited to operating non-virtual-memory systems compatible with IBM System/360 software. The first shipments of the Model 155 occurred in January of the following year.

These models featured compatibility functions supporting emulation of IBM systems such as the IBM 1401/1440/1460, IBM1410/7010, and IBM7070/7074 through integrated emulator programs capable of running alongside standard System/370 workloads.

In August of 1972, IBM released a field-upgrade-only version called System/370 Model 155 II, which added a DAT box.

Both Models were officially withdrawn on December 23, 1977.

System/370 Model 158

Announced on August 2, 1972, the IBM System/370 Model 158 and the 370/168 incorporated dynamic address translation (DAT) hardware, a critical feature for supporting the emerging virtual memory operating systems such as DOS/VS, OS/VS1, and OS/VS2. IBM provided a tightly coupled multiprocessor (MP) variant and offered an option to connect the system loosely to another 360 or 370 system via a channel-to-channel adapter. Both the Model 158 and Model 168 were officially retired on September 15, 1980.

System/370 Model 165

Introduced in April 1971, the IBM System/370 Model 165 was marketed by IBM as a "more powerful" alternative to the mid-range 370/155. It featured emulation capabilities for IBM’s earlier 700/7000 series machines, including models 7070/7074, 7080, and 709/7090/7094. The Model 165 represented a technological link between the 360/85 and subsequent systems through its microcoded control design. In August 1972, IBM launched the System/370 Model 165 II as a field upgrade that incorporated DAT hardware. The Model 165 was discontinued on December 23, 1977.

System/370 Model 168

The IBM System/370 Model 168 provided up to eight megabytes of main storage—twice that of the 370/158—and included DAT hardware to enable virtual memory functionality. As IBM’s premier system at the time, it underwent performance improvements in reaction to competition from Amdahl, including the release of an enhanced 168-3 processor variant several months earlier. The Model 168 remained operational until its withdrawal in September 1980.

System/370 Model 195

Unveiled on June 30, 1970, the IBM System/370 Model 195 stood as IBM’s most advanced computer system during that period. It followed the 360/195 by roughly fourteen months. Both versions of the Model 195 were retired on February 9, 1977.

System/370-compatible

Beginning in 1977, IBM introduced new systems identified as "compatible members of the System/370 family."

IBM 303X

The first high-end model in this series was IBM’s 3033, announced on March 25, 1977, with deliveries commencing the following March. Alongside this release, a multiprocessor variant was made available. Nicknamed "The Big One," the 3033 outperformed IBM’s previous flagship, the System/370 Model 168-3.

The IBM 3031 and 3032 were announced on October 7, 1977, and both were withdrawn on February 8, 1985.

IBM 308X

The IBM 308X lineup consisted of three high-performance models:

The 3081, announced November 12, 1980, equipped with two CPUs
The 3083, announced March 31, 1982, featuring a single CPU
The 3084, announced September 3, 1982, offering four CPUs

Despite what their numbering might imply, the least powerful unit was the 3083; it could be upgraded in the field to a configuration matching the more powerful two-CPU 3081. The four-CPU model, the 3084, represented the top-tier option.

These models introduced IBM’s Extended Architecture with support for 31-bit addressing and were compatible with MVS/Extended Architecture (MVS/XA) software—part of OS/VS2 Release 3.8—including:

Number	Name
565–279	Basic Telecommunications Access Method/System Product (BTAM/SP)
5668–978	Graphics Access Method/System Product (GAM/SP)
5740-XC6	MVS/System Product - JES2 Version 2
5685–291	MVS/System Product - JES3 Version 2
5665–293	TSO Extensions (TSO/E) for MVS/XA
5665–284	MVS/Extended Architecture Data Facility Product (DFP) Version 1

All three IBM models in the 308X series were withdrawn from service on August 4, 1987.

IBM 3090

Introduced on February 12, 1985, the IBM 3090 series debuted with the 200 and 400 models, featuring two and four processors respectively. IBM subsequently broadened the series by adding models 120, 150, 180, 300, 500, and 600, which covered a spectrum from lower to higher processing capacities; the initial digit denoted the number of CPUs.

Starting with the E models and continuing through the J and S variants, IBM incorporated Enterprise Systems Architecture/370 (ESA/370), Processor Resource/System Manager (PR/SM), along with MVS/Enterprise System Architecture (MVS/ESA) software that maintained backward compatibility while superseding earlier systems:

Number	Name
5685–279	BTAM/SP
5668–978	GAM/SP 2.0
5685–001	MVS/System Product-JES2 Version 3
5685–002	MVS/System Product-JES3 Version 3
5665–293	TSO Extensions (TSO/E) for MVS/XA
5685–285	TSO/E Version 1 Release 4
5685–025	TSO/E Version 2
5665–284	MVS/XA Data Facility Product (DFP) Version 1
5665-XA2	MVS/XA Data Facility Product (DFP) Version 2.3
5665-XA3	MVS/DFP Version 3.1

In response to rising interest in vector and array processing technologies driven by competitors such as Cray and Control Data Corporation (CDC), IBM introduced an optional vector facility (VF) extension for the 3090 series.

The initial models, 200 and 400, were discontinued on May 5, 1989.

IBM 4300

The IBM 4300 series was launched on January 30, 1979, aimed at mid-range to entry-level markets with compact processors compatible with System/370 architecture. The first offerings included models 4331 and 4341; the former was retired in November 1981 and the latter in February 1986.

Additional additions to this family comprised the 4321, 4361, and 4381 models. The 4361 introduced a "Programmable Power-Off" function enabling users to shut down the processor through program control; similarly, the 4381 featured a "Unit power off" capability.

Encompassing various model groups and versions, IBM's 4300 lineup ranged from the basic-level 4331 to the high-performance and versatile intermediate system processors represented by the 4381. Notably, the Model Group 3 of the 4381 supported dual-CPU configurations, enhancing its processing power.

IBM 9370

Announced on October 7, 1986, this entry-level system was designed to fulfill IBM customers' demand for System/370 compatibility combined with a compact size and quiet operation suitable for office settings. IBM highlighted its focus on affordable entry-level software pricing along with reduced expenses related to support, training, power consumption, and maintenance.

Targeting small to medium-sized enterprises, the IBM 9370 offered straightforward scalability through additional features and racks to meet increasing computational requirements. Introduced amid strong competition from Digital Equipment Corporation’s VAX systems, it was labeled by some in the press as a "VAX Killer," though this characterization was often met with skepticism.

Clones

Throughout the System/360 period, multiple manufacturers adopted elements of IBM/360’s instruction set and architecture to varying extents. Prominent producers included Univac with their UNIVAC 9000 series, RCA’s Spectra 70 line, English Electric’s System 4, and the Soviet ES EVM series. Except for Soviet reverse-engineered versions, these systems were neither fully compatible nor intended to be so.

With the advent of IBM/370 in the early seventies and Gene Amdahl's establishment of his own company, Japanese firms also entered the mainframe arena. Initially competing against both IBM and members of the BUNCH consortium (Burroughs, Univac, NCR, Control Data Corporation, Honeywell), Japanese efforts eventually concentrated exclusively on producing IBM-compatible mainframes.

Significant clones produced during this era included:

Architecture details

IBM's documentation assigns bit numbers starting from the most significant bit as bit 0, counting down to the least significant.

The S/370 architecture represents a computer system specification that directly evolves from the System/360 design, maintaining substantial backward compatibility. It outlines required and optional interfaces for implementations, emphasizing functional behavior instead of specifying hardware configurations.

Principal architectural characteristics include:

Big-endian byte order
One or multiple processors featuring:
- Sixteen 32-bit general-purpose registers
- Sixteen 32-bit control registers
- Four 64-bit floating-point registers
- A 64-bit Program Status Word (PSW) containing interrupt masks, privilege levels, condition codes, and a 24-bit instruction address
- Timing mechanisms and an interrupt system with both maskable and non-maskable categories
- An extensive instruction set that defines execution processes and exception handling
Memory subsystem specifications comprising:
- 8-bit bytes
- Key-based protection and 24-bit addressing capabilities
Manual control functions such as bootstrap (Initial Program Load), operator interrupts, system resets, debugging tools, and system state adjustments
An Input/Output architecture that specifies interfaces but leaves device details undefined

Optional components encompass Dynamic Address Translation (DAT) for virtual memory implementation and floating-point instruction support.

IBM emphasized maintaining compatibility for unprivileged (problem state) applications during architectural advancements. Certain enhancements aimed at boosting performance for specific operating systems without compromising compatibility include:

ECPS:MVS – optimizations tailored for MVS/370 environments
ECPS:VM – improvements designed for VM operating systems

Additional modifications targeted privileged programs but remained limited in scope with well-defined boundaries, such as:

ECPS:VSE – upgrades intended for DOS/VSE systems
S/370-XA – introduced a revamped I/O interface alongside support for 31-bit virtual and physical addressing

The architecture’s design principle guarantees that properly constructed programs developed for earlier versions operate correctly on newer platforms. For instance, bit 32 of the PSW was initially mandated to be zero; in S/370-XA, this bit signals whether addressing is 24-bit or 31-bit, facilitating backward compatibility. Subsequently, the z/Architecture incorporated a mode bit enabling 64-bit addressing while preserving compatibility across generations.

Nonetheless, some interfaces are not entirely compatible; supervisor-level control programs often require adaptation due to altered control interfaces. For example, the redesign of the I/O interface in S/370-XA made previous S/370 I/O operations incompatible without modification.

S/370 replacement

In the 1990s, IBM replaced the System/370 series with the System/390, evolving the architecture from ESA/370 to ESA/390 through incremental upward-compatible enhancements.

The year 2000 saw the System/390 succeeded by the zSeries (currently IBM Z), which introduced the 64-bit z/Architecture, representing the most substantial architectural shift since transitioning to 31-bit addressing. Throughout these generations, fundamental backward compatibility with the original S/360 architecture and instruction set has been preserved.

GCC and Linux on the S/370

The GNU Compiler Collection (GCC) originally included support for an S/370 back end, which was eventually phased out and superseded by the S/390 back end. Although the instruction sets for S/370 and S/390 have remained largely compatible since the System/360 era, GCC no longer maintains support for these earlier platforms. Presently, GCC is designed to target processors featuring the complete instruction set of System/390 Generation 5 (G5), which serves as the foundation for Linux on IBM Z. Nonetheless, an independently maintained variant, GCCMVS (version 3.2.3), continues to be accessible specifically for the S/370 environment.

Transition of I/O from original S/360 to S/370

Block multiplexer channels, which were initially restricted to models such as the 360/85 and 360/195, became a standard component within the S/370 architecture. These channels could also function as selector channels to maintain backward compatibility. They were available in configurations supporting either single-byte transfers at 1.5 MB/s or double-byte transfers at 3.0 MB/s.

Advancements in I/O following original S/370

With the introduction of Dynamic Address Translation (DAT), IBM implemented Indirect Data Address Lists (IDALs) as a feature for managing I/O memory.

Data streaming channels began with a throughput of 3.0 MB/s over a single-byte interface, which was subsequently enhanced to achieve speeds of 4.5 MB/s.

Channel set switching allowed one processor within a multiprocessor system to take over I/O responsibilities from another processor during instances of failure or scheduled maintenance.

The System/370-XA generation brought forth a channel subsystem that relieved the operating system from managing I/O queuing tasks.

The System/390 introduced the ESCON channel, an optical fiber based half-duplex serial channel capable of reaching distances up to 43 kilometers. Initially operating at 10 MB/s, its speed was later increased to 17 MB/s.

Subsequently, FICON became the predominant channel technology for IBM mainframes; FIbre CONnection is IBM’s proprietary implementation of the ANSI FC-SB-3 protocol over a Fibre Channel network, supporting data transfer rates up to 16 Gbit/s across distances as long as 100 kilometers. The Fibre Channel Protocol (FCP) enables connection of SCSI devices using this infrastructure alongside FICON.

References

S370-1st
S370
S370-MVS
S370-VM
S370-XA-1st
S370-XA
S370-ESA
S/390-ESA
SIE

External links

Hercules System/370 Emulator – A software-based implementation of the IBM System/370