Rom; Ram; Dma - IBM 5150 Technical Reference

ROM
The system board supports both Read Only Memory (ROM) and
Random Access Memory (RAM). It has space for up to 512K of
~
ROM or Eraseable Programmable ROM (EPROM). Six module
sockets are provided, each of which can accept an 8K or 8 byte
device. Five sockets are populated with 40K of ROM. This
ROM contains the cassette BASIC interpreter, cassette operating
system, power-on self test, Input/Output (I/O) drivers, dot
patterns for 128 characters in graphics mode, and a diskette
bootstrap loader. The ROM is packaged in 28-pin modules and
has an access time of 250-ns and a cycle time of 375-ns.
RAM
The RAM on the system board is as shown in the following chart.
System Board Minimum
Maximum
Memory Soldered
Pluggable
Storage Storage Modules
(Bank 0) (Bank 1-3)
64K by 1 Bank 3 Banks
64/256K 64K 256K 1 Bit of
9
of
9
Memory greater than the system board's maximum is obtained by
adding memory cards in the expansion slots. All memory is
parity-checked and consists of dynamic 64K by 1 bit chips with
an access time of 250-ns and a cycle time of 410-ns.
DMA
The microprocessor is supported by a set of high-function support
devices providing four channels of 20-bit direct-memory access
(DMA), three 16-bit timer/counter channels, and eight
prioritized interrupt levels.
System Board 1-13