Memory Modules
Memory modules
Figure 6-2.—Memory module/unit.
are made up of multiple pcb’s
(support circuitry) and memory components (stacks
[core or film] or semiconductor pcb’s with support
circuitry) to form one memory module or unit. Figure
6-2 is an illustration of a large memory module; one of
four to a single computer set. Memory modules are
interchangeable with other modules of the same type
and size in the same computer set. Each module
provides a fixed number of memory words with a fixed
number of bit positions for each word. Some memory
modules are designed with the capability to receive
requests from more than one central processing unit or
I/O section. These multiported memory modules
process memory requests on a priority basis. While the
module is processing a request from one section, the
remaining possible requesters are locked out, so to
speak, by the module logic until the completion of the
pending request.
If two requests are received
simultaneously, then the highest priority requester is
cycled first. Memory modules may contain magnetic
or semiconductor memory types. Some computers use
both but in different modules. The size of memory in
terms of bits and arrangement contained on each of
these types depends on the requirements and design of
the computer. Consult your technical manual for the
exact size and arrangement.
Memory Pcb’s
Computers that use a small number of pcb’s as their
memories are usually of the semiconductor type. In
mainframe semiconductor memory, pcb’s and support
circuitry are contained in a module or unit. In
minicomputers and microcomputers, memory can be
contained on as few as one pcb, or as many as
half-a-dozen pcb’s. When there is more than one pcb,
they are usually arranged in a group together in the
computer’s frame or cabinet. Micros can also use a
bank of IC chips for their memories. The IC chips are
mounted on single inline memory modules (SIMMs)
(fig. 6-3), single inline packages (SIPS), or single inline
Figure 6-3.—Illustration of a 30-pin single inline memory
module (SIMM).
6-3
