SC-40 Computer Systems

The SC-40 is a very high-performance system. Its CPU can run at an average rate up to 8 times that of the DEC KL10, yet a complete system -- CPU, memory, and I/O channels -- fits in a standard 20-inch cabinet.

Another important benefit of the SC-40 is its modular expansion capability; both memory and I/O channels can easily be added in the field. Compared to the KL10 processor, these systems have much lower requirements for floor space, power, air conditioning, and maintenance. Over the anticipated lifetime of a system, this results in substantial cost savings.

Technical Description: SC-40 Computer

Each single processor SC-40 offers up to eight times the performance of a single processor KL10. The base SC-40 System includes 4 megawords of Random Access Memory (RAM) and two channels (one EX and one dual-port SX).

The CPU is compatible in user mode with the DEC KL10 and is capable of performing a typical instruction mix up to 8 times faster than a KL10. The I/O channels can sustain an aggregate data transfer rate of approximately 50 million eight-bit bytes per second.

To achieve this performance, the connections between CPU, memory, and channels are strictly internal to the unit. There are no external memory or I/O busses.

The system has only one backplane, which is used for CPU, memory, and I/O interfaces. All external connections are through cable assemblies which can be easily replaced or reconfigured. Due to the modular design of this system, additional memory and I/O channels can be easily added in the field.

For console, bootstrap, and diagnostic functions each system contains a 32-bit microprocessor. It communicates with extensive diagnostic hardware in the CPU, memory units, and I/O channels.


SC-40 CPU performance will vary depending on which particular instructions are being performed, but running some typical programs, the CPU can operate approximately 8 times faster than a KL10. This means that a CPU will typically perform instructions at a rate exceeding 12 MIPS (million instructions per second).

The CPU is fully compatible in user mode with the extended- addressing KL10, including string instructions, the single- word global byte pointer, and G-format floating point. In floating-point operations, the result may differ but will always be at least as accurate as the KL10 result. TOPS-10 and TOPS-20 can be run on the SC-40 with full user-mode compatibility.

The CPU has a 32K-word write-through cache, with special logic which eliminates the need for cache sweeps. The SC-40 CPU pager uses a page table with 2048 entries (1024 for user mode and 1024 for executive).

The CPU has a full 32K words by 80 bits of control memory for firmware. This is all read/write, to facilitate the implementation of new or improved data formats and CPU instructions.


An SC-40 system has a memory capacity of up to 64M words.

The SC-40 uses a 30-bit virtual address, comprising 4096 sections of 256K words each. Performance of a process is not reduced by pager contention until its size exceeds two sections.

The memory has ECC bits to ensure single-error correction and double-error detection, as well as detecting most errors of more than two bits. All errors can be reported. The memory has numerous diagnostic features to facilitate test, checkout, and maintenance.


The SC-40 channel group can hold up to six channels, each of which can transfer data between memory and an I/O controller or device.

The CI (Computer Interconnect) channel can transfer data at rates up to 70 million bits per second, in accordance with the DEC Computer Interconnect standard. This channel can be used for high-speed transfers to other computer systems.

For connecting to industry standard equipment and networks, the EX channel provides an Ethernet interface, conforming to Revision 2 of the Ethernet specification, and operating at a rate of 10 million bits per second.

An SA (Subsystem Adaptor) channel, which offers an IBM- compatible channel interface in conformance with FIPS PUB 60-1, is available. A wide variety of peripherals can be connected to this an interface, including control units for magnetic tape drives, disk drives, laser printers, and unit record equipment. SA channels each have a maximum transfer capacity of 3 million eight-bit bytes per second.

The FX (FDDI) channel utilizes twisted-pair wiring and conforms to ANSI standard X3T9. This channel is capable of transferring data at a 100 million bit per second rate and can used for connecting to an industry standard network backbone.

Each dual-port SX (SCSI) channel conforms to ANSI standard X3.131-1986. Both SCSI I as well as SCSI II asynchronous and synchronous transfers are supported on each port at a sustained transfer rate of up to 10 million bytes per second. This interface supports industry standard SCSI devices including disk drives, reel to reel tape, and 4mm DDS-2 DAT drives.

Diagnostic Microprocessor

A 32-bit SPARC processor running at a 25 MHz clock rate performs console, supervisory, and diagnostic functions for the entire system. It performs error logging and analysis, and controls the loading of diagnostic programs and CPU firmware. In addition, this processor can be directed to vary the system clock speed or power supply margins.

During normal operation this supervisory processor monitors the cabinet temperature and power-supply output voltages; if these readings exceed normal limits the SPARC posts a warning, and if necessary shuts the system down in an orderly manner.


Except for the main processor chip, all logic and memory elements in the SC-40 are standard commercially available parts. These parts are mounted on plug-in controlled- impedance printed circuit boards, each of which can easily be removed or replaced for maintenance purposes. These boards, and the system backpanel, have four or more layers, including inner ground and power planes.

The system is packaged in one cabinet which is 20 inches wide, 30 inches deep, and 60 inches tall. Three feet of access depth is required at the front and rear for servicing, but side access is not necessary. The system consumes at most 500 watts of power, and requires 1,800 BTU of conventional computer-room air cooling.