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+---
+geometry:
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+- twoside
+papersize: A4
+...
+
+## SIC Machine Architechture
+
+### Memory
+
+- 32,768 ($2^{15}$) bytes in memory
+- All addresses are byte addresses and words are addresssed by the location
+  of their lowest numbered byte.
+
+### Registers
+
+- Each register is 24 bits in length
+
+![Registers of basic SIC](img/sic-basic-registers.png){width=70%}
+
+### Data Formats
+
+- Integers are stored as 24-bit binary numbers
+- There is no floating point in basic SIC
+
+### Instruction Formats
+
+- The flag bit $x$ is used to indicate indexed-addressing mode.
+
+![Instruction format for basic SIC](img/sic-basic-instfmt.png){width=50%}
+
+
+### Addressing Modes
+
+- two addressing modes available indicated by the $x$ bit
+- (X) means the contents of the register X
+
+![Addressing modes for basic SIC](img/sic-basic-addressing-modes.png){width=50%}
+
+
+### Input and Output
+
+- On the standard version of SIC, input and output are performed by
+  trasferring 1 byte at a time to or from the rightmost 8 bits of 
+  register A.
+- Each device has a 8bit code
+- There are three I/O instructions
+- Test Device (`TD`) tests whether the addressed device is ready; `CC`
+  is set to indicate the result ( < means the device is ready; = means
+  it's not ready)
+- `RD` and `WD` are used to read and write data to the device. Reading
+   will store a byte into register A from the device and writing will
+   transfer a byte from register A to the device
+
+
+## SIC/XE Machine Architecture
+
+### Memory
+
+- Max memory available on SIC/XE system is 1 megabyte ($2^{20}$ bytes).
+
+### Registers
+
+![Additional registers in SIC/XE](img/sic-xe-registers.png){width=65%}
+
+
+### Data Formats
+
+- Additional 48 bit floating-point data type
+
+![Floating point format](img/floating-point-format.png){width=50%}
+
+- The fraction is interpreted as a value between 0 and 1; ie, the binary point
+  is assumed to be just before the high-order bit of the fraction.
+- For normalized flaoting-point numbers, the high-order bit of the fraction
+  must be 1.
+- The exponent is an unsigned binary number between 0 and 2047
+- If $f$ is the fraction and $e$ is the exponent, then the absolute value of
+  the number represeted is: $$f\times 2^{(e-1024)}$$
+
+
+### Instruction Formats
+
+- SIC/XE provides 4 formats of instructions (Refer Appendix A)
+
+
+### Addressing Modes
+
+- Format 3 and 4 have flags to specify different addressing modes.
+- Two new relative addrssing modes are available for use with *Format 3*
+
+![Relative addressing used with format 3](img/format-3-relative-addressing.png){width=70%}
+
+- In Format 3, for _base relative_ addressing _disp_ field is interpreted as a
+  12-bit unsigned integer.  For _program-counter relative_ addressing _disp_
+  field is interpreted as a 12-bit **signed** integer, with negative values
+  represented in 2's comp.
+- In Format 3, If _b_ and _p_ are set to zero then _disp_ is the target
+  address. In Format 4, _b_ and _p_ are normally zero and the target address is
+  taken from the address field.
+- Any of theses modes can be combined with _indexed_ addressing; if bit _x_ is
+  set to 1, then (X) is added in target address calculation.
+- **Immediate and Indirect addressing** \
+  \- In Format 3 and 4, if bit _i_=1 and _n_=0 then the target address is
+  itself used as the operand value.(**i**mmediate addressing)\
+  \- If bit _i_=0 and _n_=1, the word at the location given by the target address
+  is fetched; the _value_ contained in this word is then taken as the _address_
+  of the operand value (i**n**direct addressing)\
+  \- If _i_ and _n_ are both 0 or 1 then then the target of the address is taken
+  as the location of the operand (simple addressing)\
+  \- **Indexing cannot be used with immediate or indirect addresssing**\
+  \-SIC/XE assemblers will default to 1 for both _i_ and _n_ if the
+  instructions do not specify immediate or indirect addressing modes.\
+  \-**Standard SIC assemblers will set the _i_ and _n_ bits both to zero
+  (this is because all the 8-bit binary codes for SIC instructions end with
+  00); if bits _n_ and _i_ are both 0, then the bits _b_, _p_, and _e_ are
+  considered to be part of the address field of the instruction. This makes
+  Format 3 identical to the format used on the standard version SIC, providing 
+  desired compatibility**
+
+![SIC/XE adressing modes example](img/sic-xe-addressing-modes-example.png)
+