diff --git a/sd/README.md b/sd/README.md
index 355771c..54c71b2 100644
--- a/sd/README.md
+++ b/sd/README.md
@@ -1,2 +1,11 @@
 ## `sd` package
 
+File map:
+* `blockdevice.go`: Contains logic for creating an `io.WriterAt` and `io.ReaderAt` with the `sd.BlockDevice` concrete type
+     from the `sd.Card` interface which is intrinsically a blocked reader and writer. 
+
+* `spicard.go`: Contains the `sd.SpiCard` driver for controlling an SD card over SPI using the most commonly available circuit boards. 
+
+* `responses.go`: Contains a currently unused SD response implementations as per the latest specification.
+
+* `definitions.go`: Contains SD Card specification definitions such as the CSD and CID types as well as encoding/decoding logic, as well as CRC logic.
diff --git a/sd/card.go b/sd/spicard.go
similarity index 100%
rename from sd/card.go
rename to sd/spicard.go