through the sense/digit line generating a magnetic field that  is  perpendicular  to  the  transverse  field.  The direction of the current pulse generated up and down this  line  and  the  resulting  longitudinal  field  are determined by whether a zero or a one is to be written. Frame B of figure 6-23 illustrates the bit steering to store a zero. For a write operation the film’s magnetic vector  is  first  put  in  the  hard  direction  from  the transverse field. A small longitudinal field is then applied  bypassing  a  current  through  the  sense/digit  line in the proper direction. This longitudinal field steers the vector toward the zero state. The word current is then   removed,   which   further   accelerates   the magnetization towards the zero state. Then the digit current itself is removed leaving the film in the zero state. Frame C of figure 6-23 shows that when a one is to be stored, the bit current in the sense/digit line is reversed indirection from that used to store a zero. The resulting longitudinal field now steers the vector to the one  state. READ/WRITE  CYCLE  CIRCUITS.  —Three very important circuits used in mated film memories during the read/write (restore) cycles are as follows: Word current generator—The  word  current generator produces the current pulse that provides the switching field for the memory film elements. The current generator is also used to produce drive pulses used for strobing during the memory cycle. Digit drivers—The digit drivers supply pulses required  to  write  or  restore  data  during  the  write/restore portion of all full memory cycles. Input to the drivers is supplied by the output of the data register’s flip-flops. With these signals, the digit drivers are enabled to generate drive pulses, which write alogic high or a logic low in the address bit location in accordance with the binary (one or zero) contents of the data register. The binary value determines the direction of the digit current on the sense/digit line. Sense amplifiers —Similar to core memory, the sense amplifiers sense the state of the data contained in the film element for storage in a data register for transmission of the data word or restoration of a one or a zero. Selected bits in the address register determine which group of bits are transmitted as a data word or changed by a memory write cycle. SEMICONDUCTOR  MEMORY Semiconductor  random  access  memory,  or  RAM, as it is often referred to, is used in all types of computers. RAM  is  also  called  a  read/write   memory   or a scratch-pad memory. Semiconductor RAM refers to semiconductor IC memories that can be used in a read mode  as  well  as  a  write  mode.  Semiconductor memories use either a read cycle or a write cycle depending on the type of request, independent of each other. The read cycle is normally a shorter time period than the write cycle. Semiconductor  memories  are  normally  non- destructive  readout  and  volatile  memories.  In  a nondestructive readout memory, the data stored in memory is not destroyed by the procedure used to read the  data  from  the  memory  cells.  Volatile  memories require electrical power to maintain storage. If the power goes away for some reason, the data stored in  the  memory  cells  is  lost.  For  this  reason,  an uninterruptible power supply (UPS) and a battery backup  system  are  used  in  many  semiconductor memory  applications  to  maintain  constant  power  and prevent   loss   of   information   because   of   power fluctuations or failures. This is especially important in microcomputers   where   configuration   data   is maintained  in  special  devices  such  as  a  complementary metal-oxide  semiconductor  (CMOS).  The  battery backup and a filter capacitor provide the required power when the microcomputer has been powered down. Computers that use an  UPS system  have  an  established time in which data will be retained for momentary power losses. The term random access memory (RAM) is con- sistently  used  for  read/write  devices.  Although  RAM only describes one characteristic of read/write devices, it is used and understood by most people to mean read/ write devices. RAM means random addresses can be presented  to  the  memory  which  means  data  can  be  written and read in any desired order from any location. Note: The term RAM is not used for read-only   memories (ROM), although a ROM can also be random access. Let’s   explore   the   basic   building   block   of semiconductor memories: the RAM chip. Then we discuss  the  two  main  types  of  semiconductor  RAM memories:  static  RAM  (SRAM)  and  dynamic  (DRAM), and variations of the two. SRAMS are faster but require more logic than DRAMS; thus they are more expensive than DRAMS. The RAM Chip In  semiconductor  memories,  the  basic  building block is the RAM chip (fig. 6-24). This is true whether the memories are static or dynamic memories and are pcb’s in a memory module or a pcb or pcb’s mounted singularly. The semiconductor RAM itself is made up 6-20