CMSC 1041 Machine Architecture An Introduction to Computer Components

CMSC 1042 Major Computer Components l Central Processing Unit (CPU) l Bus l Main Memory (RAM) l Secondary Storage l I / O Devices l Starting the computer

CMSC 1043 CPU l Central Processing Unit l The Brain l Controls all other computer functions

CMSC 1044 The Bus l As you can see from the diagram, the computer is made up of different components, like the CPU and main memory. l The components are connected by the bus l A bus is a group of parallel wires that carry control signals and data between components

CMSC 1045 Main Memory l Main memory is made up of capacitors l If the capacitor is charged, then its state is said to be 1 or ON. l We could also say the the bit is set. l If the capacitor does not have a charge, then its state is 0 or OFF. l We could also say that the bit is reset or cleared.

CMSC 1046 Size of Capacitors l Has decreased dramatically over the last 20 years. l Now we can fit several million capacitors on a chip the size of a dime. l As this technology becomes older, we can expect the price of memory to decrease. Is it already decreasing ? ABSOLUTELY !

CMSC 1047 Memory, the continuing saga l Memory is divided into cells, where each cell contains 8 bits. Remember that 8 bits is called a byte. l Each of these cells are numbered. l The number associated with a cell is known as its address. l Volatile storage

CMSC 1048 Reading & Writing l In addition to the circuitry that holds the bits, there are other circuits that allow other components to oGet the value of the data held at a particular address - known as a READ. oOR store data at that address - known as a WRITE.

CMSC 1049 Memory Access l All addresses in memory can be accessed in the same amount of time. l We DO NOT have to start at address 0 and read everything until we get to the address we really want. l We can go directly to the address we want and access the data. l That is why we call Main Memory RAM - Random Access Memory

CMSC Secondary Storage l Disks -- floppy, hard, removable l Tapes (sequential access) l CDs l Stores files oprograms odata files (binary, text) oDirectory structure l Persistent storage

CMSC I/O l I/O is handled by peripheral devices. l A peripheral device is some machine that is not an integral part of the computer. l Examples: oMonitor oKeyboard oDisk Drive oPrinter

CMSC Bits, Bytes and Words l A byte is 8 bits l A word is 32 bits or 4 bytes l Long word = 8 bytes = 64 bits l Quad word = 16 bytes = 128 bits l Programming languages use these standard number of bits when organizing data storage and access. l What do you call 4 bits ?? (hint: it is a small byte)

CMSC More Bits and Bytes l There are 16-, 32-, and 64-bit machines l All of UMBC Unix systems are 32-bits

CMSC Booting the Computer l The term boot comes from the expression pulling yourself up by your bootstraps. l It refers to the computers start-up procedure. l When the computer is first turned on, it reads start-up instructions found in the ROM chips.

CMSC Booting the Computer (continued) l These instructions cause the computer to do a series of tests. Each of the components is tested. l The last thing that happens during boot is that the operating system is loaded from the hard disk. l The computer cannot do anything until the operating system is loaded, because the operating system manages all of the basic functions of the computer.